The present invention relates to a mobile telecommunication system adapted by a Code Division Multiple Access (CDMA) scheme of a digital cellular system (DCS) or a personal communication system (PCS); and, more particularly, to a method of dynamically allocating a traffic channel element at an extended coverage of a base transceiver station which is divided by a cell site modem (CSM) ASIC in a mobile communication system.
FIG. 1 shows a general mobile telecommunication system adapted by a CDMA scheme of a digital cellular system (DCS) or a personal communication system (PCS). As shown in FIG. 1, the mobile telecommunication system comprises a mobile station 1, a base transceiver station 2, a base station controller 3 and a mobile switching center 4. The base transceiver station 2 receives or transmits data from/to the mobile station 1 and controls the operation of the reception and transmission. The base station controller 3 receives or transmits data from/to the base transceiver station 2 and controls the operation of the reception and transmission.
The above described mobile telecommunication system utilizes a global positioning system (GPS) to synchronize a timing thereof. All of mobile stations generate signals according to a reference clock signal.
Each of the generated signals is delayed according to a moving distance thereof. Therefore, a phase delay phenomenon is generated in each of the signals. In order to overcome the phase delay phenomenon, each of the stations receiving the phase delayed signal has to perform an exact phase tracking to demodulate the received signal.
However, the cell site modem ASIC, which is contained at a channel card of the base transceiver station 2 and used as a channel element (CE), has 512 PN chip of a phase tracking boundary (1 PN chip=813 nsec). The 512 PN chip can be represented as 125 Km of a radio wave moving distance.
Since the 125 Km represents the distance of a radio wave running between the base transceiver station 2 and the mobile station 1, a call possible coverage becomes within the radius of 62.5 Km centered from the base transceiver station 2.
Accordingly, the coverage of the mobile telecommunication system of one cell site modem ASIC is limited to 60 Km. In general, a cell area of the downtown is within the radius of 7 Km according to a capacity of the mobile telecommunication system.
However, in order to provide a mobile telecommunication service in a country area such like a coastal area or an island area, a pair of cell site modem ASICs is used to extend the call possible coverage. The pair of cell modem ASICs is made with a simple hardware modification and a software control. Accordingly, it is not necessary to redesign the cell site modem ASIC.
That is, a phase tracking of the cell site modem ASIC at a normal region within 60 Km is possible with zero to 512 PN chip. Another phase tracking of the cell site modem ASIC at an extended region from 60 to 120 Km is possible with 512 to 1024 PN chip.
As described above, the call coverage is divided into the normal region and the extended region according to the cell site modem ASIC. At this time, in case that the mobile station moves from the normal region to the extended region or moves from the extended region to the normal region, a common region or a handoff region has to be necessary so as to enable both the cell site modem ASICs to perform the phase tracking.
Accordingly, the call coverage is divided into the normal region, the handoff region and the extended region. And, a various point is set according to the movement of the mobile station. In case that the mobile station moves from the normal region to the extended region, an Extended Call Add Point, a Normal Call to Extended Call Swap Point, a Normal Call Drop Point are set. On the contrary, in case that the mobile station moves from the extended region to the normal region, a Normal Call Add point, an Extended Call to Normal Call Swap Point, and an Extended Call Drop Point are set.
In addition, an access channel of the handoff region is determined by an intermediate value of a round trip delay (RTD). In case that a value is less than the intermediate value, it is processed as the access channel of the normal region. In case that another value is larger than the intermediate value, it is processed as the access channel of the extended region.
However, the prior mobile telecommunication system has to utilize both the cell site modem ASICs as one pair of channel elements in order to perform the above described call process in the extended coverage of the base transceiver station. Although each of call processes at a normal region and the extended region, excluding the call process at the handoff region, needs only the one of the pair of channel elements, the other cannot be utilized. And thus, there occurs an unnecessary channel allocation.
It is, therefore, a primary object of the invention to provide a method for dynamically allocating a traffic channel element at an extended coverage of a base transceiver station which is divided by a cell site modem (CSM) ASIC in a mobile communication station. In case that the call coverage is divided into a normal and an extended regions, the traffic channel element is not set to a pair of the normal and the extended channel elements. Instead, the channel allocation is dynamically allocated according to a channel type which is necessary on a call set up at each of the regions. Thereby, it is possible to reduce an unnecessary channel allocation and an occupation time of the channel element.
In accordance with the present invention, there is provided a method of dynamically allocating a channel at an extended coverage of a base transceiver station in a mobile communication system, comprising the steps of: (a) measuring, in case that a call setting requirement or a page response is received from the base transceiver station, a round trip delay (RTD) value at a channel element (CE) of the base transceiver station to report a measured RTD value to a transcoder and selector bank (TSB) of a base station controller; (b) confirming a position of the mobile station based on the measured RTD value and determining a CE allocation type corresponding to the position of the mobile station; (c) if the RTD value is larger than a cutoff, recognizing that the mobile station is located within an extended region, thereby allocating an extended CE; (d) performing an extended call process by using the extended CE; (e) if the RTD value is less than the cutoff, recognizing that the mobile station is located within a normal region, thereby allocate a normal CE; and (f) performing a normal call process by using the normal CE.
The method for dynamically allocating a channel at an extended coverage of a base transceiver station in accordance with the present invention further comprises the steps of: (g) comparing, during the normal call process according to a normal channel allocated in step (e), the RTD value to an extended add value, and, performing, in case that the RTD value is larger than the extended add value, an extended add operation to additionally allocate an extended channel, and, otherwise, returning to the step (f); (h) comparing the RTD value to a swap-to-extend value, performing, in case that the RTD value is larger than the swap-to-extend value, a region swap operation to enable the normal channel to be inactive and simultaneously to enable the extended channel to be active, and performing, in case that the RTD value is less than the swap-to-extend value, comparing the RTD value to the swap-to-extend value; and (i) comparing the RTD value to a normal drop value, performing, in case that the RTD value is larger than the normal drop value, a region drop operation to enable a standby state of the normal channel allocation to be clear, and then, performing the extended call process.
The method for dynamically allocating a channel at an extended coverage of a base transceiver station further comprises the steps of: (j) comparing, during the normal call process by using the normal channel allocated in step (f), the RTD value to a normal-add value, performing, in case that the RTD value is less than the normal-add value, a region add operation to additionally allocate the normal channel, and, returning, in case that the RTD value is larger than the normal-add value, to the extended call processing; (k) comparing the RTD value to a swap-to-normal value, performing, in case that the RTD value is less than the swap-to-normal value, a region swap to enable the extended channel to be inactive, and simultaneously, to enable the normal channel to be active, and returning, in case that the RTD value is larger than the swap-to-normal value, to the step of comparing the RTD value to the swap-to-normal value; and (l) comparing the RTD value to an extend-drop value, and performing, in case that the RTD value is less than the extend-drop value, a region drop operation to enable the standby state of the extended channel allocation to be clear, and processing the normal call process.